Tool and method for the finishing of valve seats and guides

ABSTRACT

It is proposed to provide a tool for the final machining of a valve seat and valve guide in a cylinder block of a combustion engine of a motor vehicle, said tool having a first section with at least one first blade for machining the valve seat and a second section with at least one second blade for machining the valve guide. The tool is characterized in that a separation site ( 13 ) is provided between the first section ( 5 ) and the second section ( 9 ), said separation site comprising a cone ( 15 ) and a conical recess ( 17 ) capable of receiving said cone.

The invention relates to a tool for final machining of a valve seat andvalve guide in a cylinder head of a combustion engine according to thepreamble of claim 1, furthermore to a method for final machining of avalve seat and valve guide in a cylinder head of a combustion engineaccording to the preamble of claim 6.

Tools and methods for final machining of a valve seat and valve guideare known. This kind of machining involves one of the most exactingmachining in the cylinder head. In particular, the coaxiality of thevalve seat and the valve bore is a criterion for the tightness and thusthe fuel consumption of the combustion engine. Different methods existfor attaining the required precision which usually is in the range of0.025 mm maximum.

For the machining of a valve seat and valve guide on a machining center,the known methods require at least two tools, and for very smalldiameters even three tools, depending on the diameter of the valveguide. With the aid of a tool, a pilot bore is prepared in which thesubsequently inserted final machining tool moves during the cutting. Themachining time in this case is relatively long because it is necessaryfirst to prepare a pilot bore before the final machining can be done.

Another method is carried out on transfer lines. To achieve the rigidityrequired for the tool used for machining the valve guide, a feed-outspindle comprising two tools is employed. In this case, a thin toolintended for the valve guide is moveable within another tool and isguided through a bushing.

It has been established that the machining times on a machining centerare too long and that the machining on a transfer line requires veryexpensive tools in order to achieve the precision needed for themachining of a valve seat and valve guide.

Hence, the object of the invention is to provide a tool and a method forthe final machining of a valve seat and valve guide in a cylinder blockof a combustion engine that do not have these drawbacks.

To reach this objective, we propose a tool having the features stated inclaim 1. Said tool is characterized in that between a first section ofthe tool used for the machining of the valve seat and a second sectionused for the machining of the valve guide there is provided a separationsite comprised of a cone and a conical recess to receive said cone. Bymeans of this separation site, the rigidity of the tool is substantiallyincreased. Moreover, the assembly is much simpler and more economicalthan with feed-out tools.

Other embodiments of the invention are covered by the subclaims.

To reach the said objective, we also propose a method for the finalmachining of a valve seat and valve guide in a cylinder block of acombustion engine, said method comprising the features indicated inclaim 6. The method is characterized in that the final machining isperformed with a single tool. In other words, it is not necessary tocreate a pilot bore for the final machining using a preliminarymachining tool. Also, no guide bushing is needed for the finalmachining.

A preferred embodiment of the method of the invention is characterizedin that the final machining is carried out in a single step. In otherwords, creating a valve seat and valve guide in a cylinder block doesnot require a preliminary as well as a final machining.

In the following, the invention will be explained in greater detail byreference to a drawing. The single drawing shows a tool 1 in explodedside view. Tool 1 comprises a conventional shaft 3 with a slightlyconical outer contour and which serves for coupling with a tool machine.

Tool 1 comprises a first section 5 with at least a first cutting plate 7provided with a blade for machining the valve seat.

Furthermore, tool 1 comprises a second section 9 with a second cuttingplate 11 provided with a blade for machining the valve guide. The twosections 5 and 9 of tool 1 are connected to each other through aseparation site 13. Said site comprises a cone 15 provided on the secondsection 9, said cone fitting into a conical recess 17 provided on thefirst section 5 of tool 1. To cone 15 is assigned a first plane surface19, and to conical recess 17 a second plane surface 21. In the assembledcondition, sections 5 and 9 of tool 1 are placed very close to eachother in the region of separation site 13 so that the second section 9is in a defined alignment with the first section 5. By means of cone 15and conical recess 19, it is ensured that the two sections 5 an 9 aredisposed exactly coaxially to one another.

Plane surfaces 19 and 21 are preferably annular surfaces to ensure acircular contact surface for the two sections 5 and 9 of tool 1 in theregion of separation site 13.

The drawing shows that the second section 9 presents a widened region 22starting from the first plane surface 19, said region being locatedbetween the first plane surface 19 with a larger outer diameter and theactual tool 22′ of the second section 9 and here, for example directlyadjacent to the first plane surface 19, presenting a cylindrical sectionwhich conically tapers off in the direction of cutting plate 11. To thisthere may be connected another section with a cylindrical outer surfacethe outer diameter of which is larger than that of the actual tool 22′performing the final machining of the valve guide.

The widened region, also referred to as a collar, is made of the samematerial as the actual tool 22′ in order to achieve optimum toolrigidity and reduced vibration characteristics.

Separation site 13 comprises a tightening screw 23 with two threadedsections 25 and 27 the turns of which run in opposite directions.Tightening screw 23 is used to thoroughly press together the twoelements of the separation site 13, namely the two sections 5 and 9 oftool 1. When tightening screw 23 is loosened, the two sections 5 and 9of tool 1 are pushed apart so that the clamping forces between cone 15and conical recess 17 are reduced.

To accomplish the final machining of a valve seat and valve guide in acylinder block of a combustion engine, the two sections 5 and 9 of tool1 are tightened against each other in the region of separation site 13so that cone 15 enters conical recess 17 and the two plane surfaces 19and 21 are disposed close to each other. In this manner, high rigidityof tool 1 and absolutely accurate mutual lengthwise positioning ofsections 5 and 9 are achieved.

The second section 9 of tool 1 is shaped as a reamer for the machiningof the valve guide. Usually, in addition to the second cutting plate, atleast one guide gib is provided in the region of the second section 9.The drawing shows a guide gib 29 facing the observer.

It is essential for the tool described here that the first section 5 andthe second section 9 be made of different materials, steel being usedpreferentially for the first section 5 and serving for the machining ofthe valve seat, and the second section used for machining the valveguide being made of hard metal.

Compared to steel, hard metal has a higher modulus of elasticity. Hardmetals having a modulus of elasticity that is two to three times higherthan that of steel are preferably used. Thus, under the same conditionsof geometry and stress, first section 5 made of steel stretches ordeforms two to three times as much as does the second section 9consisting of hard metal.

Because the long and slim second section 9 of tool 1 is made of hardmetal, high rigidity is achieved here. The rigidity of the entire tool 1is increased even more by the combination of the described material.

Because a separation site is provided between first section 5 and secondsection 9 of tool 1 as a result of which the grain orientation withintool 1 is interrupted, vibrations induced in tool 1 by the chip removalfrom a work piece are particularly well damped.

The high rigidity of tool 1, which is based on the special materialcombination, the widened region 22 of second section 9 and theinterruption of the grain orientation by separation site 13, results inparticularly good machining quality during the machining of the valveseat and valve guide with the aid of the herein-described tool 1. Thehigh rigidity of tool 1 is further enhanced by the short cone 15 and thetwo plane surfaces 19 and 21 and also by the use of hard metal in theregion of second section 9.

In the following, the function of tool 1 and the method of finalmachining of a valve seat and valve guide in a cylinder block of acombustion engine will be discussed in greater detail.

For the purpose of final machining of the two said regions within acylinder block, the assembled tool 1 is set in rotation and is made tomove in relation to the cylinder block. It is made to move in thedirection of its rotation axis 31 so that second section 9 with secondcutting plate 11 is introduced into the bore serving as valve guide.This results in final machining of the bore surface. Finally, tool 1 isintroduced into the cylinder block to a distance such that first cuttingplate 7 of first section 5 engages the cylinder block and executes thefinal machining of the valve seat.

In other words, what is needed to accomplish the final machining of avalve seat and valve guide in a cylinder block is a single tool 1 of theherein-described design. By no means is it necessary to make a pilotbore in the cylinder block to be able to perform the final machining. Itis also not necessary to use a guide bushing to be able to ensureguidance when introducing tool 1 into the valve guide. Because of itsdesign, namely because of the presence of separation site 13 betweenfirst section 5 and second section 9, tool 1 is so rigid that the valveguide is optimally coaxial with the valve seat. Bending of tool 1 in theregion of second section 9 is much reduced compared to tools consistingof a single piece, because the rigidity of tool 1 is substantiallyenhanced by separation site 13 and by the use of hard metal for thesecond section 9.

During the final machining of a valve seat and valve guide, exactconcentricity of tool 1 is achieved, because cone 15 and conical recess17 as well as plane surfaces 19 and 21 can be fabricated to very closetolerances. As a result of the high concentricity precision whichamounts to <3 μm, alignment and imbalance problems do not arise.

The surface quality of a valve seat and valve guide are further enhancedby the fact that vibrations generated within tool 1 during the finemachining are interrupted at separation site 13, namely at thetransition site between second section 9 and first section 5, and arethus markedly damped. The vibrations can also be further reduced byusing different materials for the fabrication of the two sections 5 and9.

Second section 9 of tool 1 can be fabricated separately. As a result,particularly for small machining diameters, the quality of tool 1 issubstantially higher than that of conventional, single-piece tools.

From the explanations provided for tool 1 and the manner in which itfunctions, it is clear that the tool is of very simple design and thuscan be fabricated economically. The simple design is due to the fact,among other things, that there is no need for two partial tools that aremovable relative to each other, as is the case with feed-out tools. Thetool is characterized in that the machining of a valve seat and valveguide in the cylinder block of a combustion engine can be carried out insimple manner: Such machining can be carried out with a single tool.Thus, it is not necessary to use complicated two-part, so-calledfeed-out tools the parts of which are movable relative to each other andduring the machining of a valve seat and valve guide require separatecontrol. Moreover, it is possible to carry out the final machining of avalve seat and valve guide in a cylinder block of a combustion engine ina single machining step. In other words, it is also not necessary tomake a pilot bore to enable a subsequent final machining to be carriedout.

Furthermore, the simple design of tool 1 permits the machining ofdifferent cylinder blocks on the same transfer line. This is possiblebecause the herein-described tool can be changed automatically in simplefashion.

Finally, a universal use of tool 1 is also possible, on the one hand,because the materials used to fabricate first section 5 and secondsection 9 can be optimized for different applications. In other words,it is possible, by the selection of special damping tools, to reduce thevibrations within tool 1, vibrations that are already markedly reducedby the presence of separation site 13.

Moreover, it is possible to use tools with different sections 5 and 9.In other words, it is possible, in simple fashion, to subject valveseats and valve guides of different diameters to final machining,because first section 5 and second section 9 having different machiningdiameters can be combined with one another. The close tolerances forcone 15 and plane surfaces 19 and 21 result in high precision whendifferent sections of a tool are assembled. Moreover, in each case thehigh rigidity and the good damping properties of the tool are retained.

1. Tool for final machining of a valve seat and valve guide in thecylinder block of a combustion engine of a motor vehicle, said toolhaving a first section provided with at least one first blade formachining the valve seat and a second section provided with at least onesecond blade for machining the valve guide, characterized in that aseparation site (13) is provided between the first section (5) and thesecond section (9), said separation site comprising a cone (15) and aconical recess (17) capable of receiving said cone.
 2. Tool according toclaim 1, characterized in that the separation site (13) comprises twoplane surfaces (19, 21) of which the first one (19) is disposed on thefirst section (5) and the second one (21) is disposed on the secondsection (9).
 3. Tool according to claim 1 or 2, characterized in thatthe first plane surface (19) and/or the second plane surface (21) havethe shape of an annular surface.
 4. Tool according to one of thepreceding claims, characterized in that the sections (5, 9) of the tool(1) can be made of different materials, steel preferably being used forthe first section (5) and hard metal for the second section (9).
 5. Toolaccording to one of the preceding claims, characterized in that thesecond section (9) has a widened region (22) which is preferablyadjacent to the separation site (13).
 6. Method for final machining of avalve seat and a valve guide in the cylinder block of a combustionengine of a motor vehicle by means of a tool comprising a first sectionprovided with at least one first blade and a second section providedwith at least one second blade, particularly by means of a toolaccording to one of the preceding claims 1 to 5, characterized in thatthe final machining is carried out with a single tool.
 7. Methodaccording to claim 6, characterized in that the final machining isperformed in a single step.